Hydrogenated castor oil is a good organic thixotrope or “rheological additive” (RA) because it provides excellent performance when the additive is dispersed and activated in a specific manner. The rheological additive provides anti-settling effects, and controls flow and leveling as well as the degree of sagging in paints and coatings. The glyceride moiety in castor wax can be replaced by amine functional materials to yield wax like amides of 12-hydroxy stearic acid. These amides are also quite effective as rheological control agents, and they complement hydrogenated castor oil to yield an effective castor wax portfolio of materials for the paint formulator to choose from. The castor derived 12-hydroxystearic acid moiety is an effective rheological component because it can self-assemble into spatially preferred structures, some of which extend throughout the formulation and effectively trap solvent and/or resin and thereby control the material flow.
Prior art polyamide based rheological additives have specific processing temperature requirements that are related to the solvency effects present in a paint system or a sealant system. Therefore, the most appropriate choice of polyamide rheological additives for any given system depends on solvent type(s), processing temperature control and the manufacturing equipment. An optimal combination of these parameters allows for the most effective level of colloidal dispersion and yields a rheologically active network.
However, problems can arise when the paint processing temperature is too high for the additive—the polyamide rheological additive can dissolve completely at these elevated temperatures and later on, as the system cools down, the additive can precipitate and form semi-crystalline particulate matter, which is sometimes also referred to as “seeds”. A similar seeding situation can occur when the solvent/temperature combination is too strong. The immediate seeding effect typically can be observed relatively quickly. A more complex seeding situation may occur when the additive is not processed enough or not enough solvent is present. In these cases potentially, not all powdered wax material has been converted into the desirable rheologically active form and unused material remains behind, often unnoticed at the point of paint manufacture. Over time upon storage, this unused additive material can transform under the influence of solvent, ambient temperature and time, to yield particles that lead to loss of fineness of grind and reduced gloss of the paint system, or activate overtime to become rheologically active.
For sealant, adhesive and coating compositions, long term storage above room temperature can lead to activation of the unactive polyamide additive which results in an undesirable increase in viscosity of such composition.
The present invention provides for rheological additives that activate easily and can be used in high solids paint systems or MS polymer sealants.